Conventionally, retardation plates have been used for the purpose of optical compensation in various liquid crystal displays. For such retardation plates, for example, optical biaxial retardation plates are used. The biaxial retardation plates can be manufactured by various kinds of polymer film stretching techniques such as roller tensile stretching, roller press stretching, and tenter transverse uniaxial stretching (for example, see JP 3(1991)-33719 A), and also manufactured by the technique of biaxial stretching to provide an anisotropy (for example, refer to JP 3(1991)-24502 A), or the like. Other examples include a retardation plate including both a uniaxially stretched polymer film having a positive optical anisotropy and a biaxially stretched polymer film having a negative optical anisotropy with a small in-plane retardation value (see JP 4(1992)-19482A). Alternatively, a retardation plate provided with a negative uniaxiality can be manufactured not by any of the above-mentioned stretching methods but by using the property of polyimide so as to process a soluble polyimide into a film on a substrate (JP 8(1996)-511812 A).
Stretched films formed by the above-described film-stretching techniques are provided, for example, with an optical characteristic nx>ny>nz. Here, nx, ny, nz indicate refractive indexes in an X-axis direction, a Y-axis direction and a Z-axis direction, respectively. The X-axis corresponds to an axial direction exhibiting a maximum refractive index within a plane of the film, the Y-axis corresponds to an axial direction perpendicular to the X-axis within the plane, and the Z-axis corresponds to a thickness direction perpendicular to the X-axis and the Y-axis. When arranged between a liquid crystal cell and a polarizer of a liquid crystal display, a birefringent film having the above-stated optical characteristics can widen a viewing angle of the liquid crystal display, and thus the birefringent film is useful as a viewing angle compensating film for the liquid crystal cell.